Production of low-fogging polyurethane foams, and specific poly-oxyalkylene-polyols which can be used for this purpose

ABSTRACT

The invention relates to a process for the production of polyurethane foams by reacting 
     a) at least one organic polyisocyanate with 
     b) at least one polyalkylene-polyol (b1) having a hydroxyl number of from 30 to 500, obtainable by alkoxylation of at least one initiator molecule from the group consisting of N,N&#39;-bis(3-aminopropyl)ethylenediamine, tripropylenetetramine and tetrapropylenepentamine using at least one alkylene oxide, preferably ethylene oxide and/or 1,2-propylene oxide, or mixtures of the polyoxyalkylene polyols (b1) and other polyhydroxyl compounds having a functionality of from 2 to 8 and a hydroxyl number of from 15 to 500, and 
     c) if desired, chain extenders and/or crosslinking agents, in the presence of 
     d) blowing agents and, if desired, 
     e) catalysts and 
     f) additives, 
     and to the novel polyoxyalkylene-polyols (b1) which can be used for this purpose.

The present invention relates to a process for the production ofpolyurethane foams, also abbreviated to PU foams below, preferablysemirigid or rigid PU foams which have an improved foam structure, goodaging properties and very good flow properties of the foamable reactionmixture and which are low-fogging, by reacting organic polyisocyanates(a) with polyhydroxyl compounds (b) and, if desired, chain extendersand/or crosslinking agents (c) in the presence of blowing agents (d)and, if desired, catalysts (e) and additives (f), where, according tothe invention, the polyhydroxyl compounds (b) arepolyoxyalkylene-polyols (b1) having a hydroxyl number of from 30 to 500which are obtainable by polyaddition of at least one alkylene oxide,preferably ethylene oxide and/or 1,2-propylene oxide, onto at least oneinitiator molecule from the group consisting ofN,N'-bis(3-aminopropyl)ethylenediamine, tripropylenetetramine andtetrapropylenepentamine, or industrially obtainable crude productsthereof.

The present invention furthermore relates to the novelpolyoxyalkylene-polyols (b1) containing tertiary amino groups as bridgeswhich can be used in accordance with the invention.

The production of PU foams by reacting organic polyisocyanates withrelatively high-molecular-weight polyhydroxyl compounds and, if desired,low-molecular weight chain extenders and/or crosslinking agents in thepresence of catalysts and blowing agents and, if desired, additives andauxiliaries is known and is described in numerous patents and otherpublications. Reference may be made to the Kunststoff-Handbuch, VolumeVII, Polyurethane, 1st Edition, 1966, edited by Dr. R. Vieweg and Dr. A.Hochtlen, Carl Hanser Verlag, Munich.

Also known is the production of semirigid PU foams by the prepolymerprocess, usually from tolylene diisocyanate (TDI) prepolymers, and ofsemirigid and rigid PU foams by the one-shot process, advantageouslyusing mixtures of diphenylmethane diisocyanates (MDI) andpolyphenylpolymethylene polyisocyanates, known as crude MDI, aspolyisocyanates. A specific selection of relativelyhigh-molecular-weight polyhydroxyl compounds and chain extenders and/orcrosslinking agents and various amounts of polyisocyanates and waterallow semirigid and rigid PU foams having various mechanical propertiesto be produced by this process. Furthermore, semirigid PU foams can beproduced without using water by the frothing process with the additionof dichlorodifluoromethane as blowing agent. The polyhydroxyl compoundsused here are a combination of branched, relativelyhigh-molecular-weight polyoxyalkylene-polyols and amine-initiated chainextenders having hydroxyl numbers in the range from 450 to 500. Thepolyaddition reaction can be activated by means of organotin compounds(Kunststoff-Handbuch, Volume VII, Polyurethane, 2nd Edition, 1983,edited by D. G. Oertel, Carl Banset Verlag, Munich, Vienna).

EP-A-0 490 145 describes composite elements comprising at least oneouter layer of polyvinyl chloride or a polyvinyl chloride-containingpolymer mixture and a PU foam, preferably a semirigid or rigid PU foam.

PU foams are expediently produced with addition of tertiary amines ascatalysts, since these accelerate both the reaction between the hydroxylgroups of the polyhydroxyl compounds and the NCO groups of thepolyisocyanates, the urethane formation and the reaction between waterand NCO groups with formation of amino groups and carbon dioxide asblowing gas, the blowing reaction; in particular in the one-shotprocess, the rates of the reactions occurring alongside one another mustbe matched precisely to one another. Since crosslinking reactions withformation of allophanate, urea, biuret and cyanurate structures can alsotake place alongside the polyaddition and blowing reactions during foamformation, the catalysts employed must ensure that these variousreactions take place synchronously. The catalysts must neither losetheir catalytic activity due to premature incorporation into thepolyurethane structure nor accelerate hydrolyric decomposition of theresultant PU foam.

A disadvantage of many of the tertiary amines used as catalysts inindustry is their unpleasant odor, which is transferred to the PU foamsproduced and can adversely affect their use in certain applications.According to DE-A-23 21 884 (GB-A-1,344,038), PU foams are thereforeproduced using polyether-polyols prepared by means of a tertiary amineas catalyst in combination with an acid and a silicone oil.

Also known are highly reactive polyoxyalkylene-polyols containing bondedtertiary amino groups; according to EP-A-0 539 819, these are preparedby oxyalkylation of an initiator molecule containing at least tworeactive hydrogen atoms and at least one tertiary amino group bonded viaa spacer bridge comprising at least three methylene groups, by means ofat least one alkylene oxide. The highly reactivepolyoxyalkylene-polyols, which preferably have a functionality of 2 or 3and a molecular weight of from 2800 to 6200 and are prepared usingN,N-dimethyl-1,4-diaminobutane, N,N-dimethyl-1,3-diaminopropane andN,N-dimethyldipropylenetriamine as initiator molecules, are used for theproduction of compact or cellular, preferably flexible polyisocyanatepolyaddition products. Polyoxyalkylene-polyols of this type have highcatalytic activity in PU formulations for the production of flexible andsemirigid PU foams.

It is an object of the present invention to ensure that the variousreactions during the production of PU foams, preferably semirigid, andrigid PU foams, occur synchronously while avoiding odor nuisance duringthe foaming process and due to the resultant foam. It is a furtherobject to reduce the formation of voids in the foam and thus drasticallyto reduce the reject rate in the foam back of dashboards and othercomposite elements, for example those having top layers of polyvinylchloride and other polyvinyl chloride-containing polymer mixtures.Through the improvement in the PU foam structure, the mechanicalproperty level is to be increased and homogenized over the entire PUmolding. A further aim is to improve the flow properties of the foamablereaction mixture and to extend the processing range with respect tofoaming equipment and conditions, for example the temperatureconditions. It should be possible to modify the mechanical properties ofthe PU foams by means of suitable additives which are compatible with PUformative components. The PU foams, preferably semirigid and rigid PUfoams, should be very substantially fogging-free.

We have found that, surprisingly, this object is achieved by usingselected polyoxyalkylene-polyols initiated by means of aliphaticpolyamines as all or some of the polyhydroxyl compound.

The present invention accordingly provides a process for the productionof PU foams, preferably semirigid or rigid PU foams, by reacting

a) at least one organic or modified organic polyisocyanate or a mixtureof an organic and a modified organic polyisocyante with

b) at least one relatively high-molecular-weight polyhydroxyl compoundcontaining at least two reactive hydrogen atoms, and

c) if desired, low-molecular-weight chain extenders and/or crosslinkingagents,

in the presence of

d) blowing agents and, if desired,

e) catalysts and

f) additives,

wherein the polyhydroxyl compound (b) is a polyoxyalkylene-polyol (b1)having a hydroxyl number of from 30 to 500, obtainable by alkoxylationof at least one initiator molecule from the group consisting ofN,N'-bis(3-aminopropyl)ethylenediamine, tripropylenetetramine andtetrapropylenepentamine, or a mixture of at least two of said initiatormolecules, using at least one alkylene oxide.

The present invention furthermore provides polyoxyalkylenepolyols havinga hydroxyl number of from 30 to 500 obtainable by polyaddition of atleast one alkylene oxide onto an initiator molecule from the groupconsisting of N,N'-bis(3-aminopropyl)ethylenediamine,tripropylenetetramine and tetrapropylenepentamine and technical-grademixtures thereof.

The polyoxyalkylene-polyols containing bonded tertiary amino groupswhich can be used in accordance with the invention are catalyticallyactive and, in particular in combination with carboxylic acids,accelerate the polyaddition reaction of organic polyisocyanates withpolyhydroxyl compounds. Their addition to PU reaction mixtures, even inextremely small amounts, can cause a significant shortening of the molddwell time in the production of PU molded foams. This technicaladvantage, which also results in a reduction in production costs, is ofconsiderable importance, in particular in the production of rigid PU foemoldings. The novel polyoxyalkylene-polyols are excellent solvents forcertain blowing agents, for example (cyclo)alkanes, in particularcyclohexane, their addition enabling a considerable reduction inviscosity. In the case of rigid PU foams, their addition can reducebrittleness and, with the additional use of plasticizers for which theyare solubilizers, allow the ridigity to be adjusted as desired, i.e.according to technical requirements.

The PU foams, in particular semirigid PU foams, have excellent agingvalues and exhibit no exudation of volatile compounds.

Reaction mixtures for the production of PU foams have very good flowproperties and, in contrast to, for example, ethylenediamine-initiatedpolyoxyalkylene-polyols, do not have an adverse effect on the foamingtimes. In spite of a reduction in density, the mechanical properties ofthe odorless PU foams produced in accordance with the invention can beimproved.

The low tendency toward formation of voids in the PU foams isadvantageous and therefore noteworthy. In the foam backing of, forexample, dashboards and other composite elements, for example thosehaving top layers of polyvinyl chloride (PVC) or other PVC-containingpolymer mixtures, thermoplastic polyurethane oracrylonitrile-styrene-acrylate rubber (ASA), the reject rate can thus bedrastically reduced.

The following details apply to the novel process for the production ofPU foams, preferably semirigid and rigid PU foams, and to the startingmaterials-which can be used for this purpose:

a) Suitable isocyanates for the production of the PU foams, preferablysemirigid and rigid PU foams, are the organic, for example aliphatic,cycloaliphatic and preferably aromatic, diisocyanates and/orpolyisocyanates (a) known per se. Specific examples of aromaticpolyisocyanates are: mixtures of 4,4'- and 2,4'-diphenylmethanediisocyanate (MDI), mixtures of MDI and polyphenyl-polymethylenepolyisocyanates (crude MDI), expediently having a content of MDI isomersof at least 30% by weight, preferably from 40 to 90% by weight or more,based on the total weight of the mixture, 2,4- and 2,6-tolylenediisocyanate (TDI) and the corresponding commercially available isomermixtures, mixtures of TDI and MDI and/or crude MDI.

Other suitable organic polyisocyanates (a) are modified organicpolyisocyanates, i.e. products obtained by chemical reaction of organicdiisocyanates and/or polyisocyanates. Mention may be made by way ofexample of diisocyanates and/or polyisocyanates containing ester, urea,biuret, allophanate, isocyanurate and preferably carbodiimide,uretoneimine and/or urethane groups. Specific mention may be made of,for example: urethane group-containing prepolymers hating an NCO contentof from 14 to 2.8% by weight, preferably from 12 to 3.5% by weight, orquasiprepolymers having an NCO content of from 35 to 14% by weight,preferably from 34 to 22% by weight, where urethane group-modifiedpolyisocyanates made from TDI have, in particular, an NCO content offrom 34 to 28 % by weight and those made from 4,4'-MDI, 4,4'- and2,4'-MDI isomer mixtures or crude MDI have, in particular, an NCOcontent of from 28 to 22% by weight, based on the total weight, and areprepared by reacting diols, oxyalkylene glycols and/or polyoxyalkyleneglycols having molecular weights of from 62 to 6000, preferably from 134to 4200, with TDI, 4,4'-MDI, MDI isomer mixtures and/or crude MDI, forexample at temperatures of from 20° to 110° C., preferably from 50° to90° C., where, as oxyalkylene and polyoxyalkylene glycols, which may beemployed individually or as mixtures, mention may be made by way ofexample of: diethylene glycol, dipropylene glycol, polyoxyethyleneglycol, polyoxypropylene glycol and polyoxypropylene-polyoxyethyleneglycol, and polyisocyanates containing carbodiimide groups and/orisocyanurate groups, for example based on MDI isomers and/or TDI.

However, particular success has been achieved by, and preference istherefore given to, mixtures of 4,4'- and 2,4'-MDI, crude MDI having anMDI content of at least 30% by weight, based on the total weight,mixtures of 4,4'- and 2,4'-MDI and mixtures of 2,4- and 2,6-TDI,mixtures of crude MDI and mixtures of 2,4- and 2,6-TDI, urethanegroup-containing polyisocyanate mixtures having an NCO content of from28 to 14% by weight, based on the total weight, based on MDI and/orcrude MDI.

The organic polyisocyanates which can be used according to the inventioncan be prepared by known processes, for example by reaction of thecorresponding polyamines with phosgene to give carbamoyl chlorideintermediates, followed by thermolysis thereof to give polyisocyanates,or by phosgene-free methods, for example by reaction of thecorresponding polyamines with urea and/or carbamates and alcohols togive monomeric polyurethanes, followed by thermolysis thereof to givepolyisocyanates and alcohols.

b) The relatively high-molecular-weight polyhydroxyl compounds (b) usedaccording to the invention are polyoxyalkylene-polyols (b1) having ahydroxyl number of from 30 to 500, preferably from 200 to 450, inparticular from 250 to 410, which are obtainable by alkoxylation of atleast one initiator molecule from the group consisting ofN,N'-bis(3-aminopropyl)ethylenediamine, tripropylenetetramine andtetrapropylenepentamine, or a mixture of at least two of the saidinitiator molecules.

Said initiator molecules can be used in the form of chemically purecompounds having a functionality of from 6 to 8, as industriallyobtainable compounds or in the form of an industrially obtainablemixture contaminated by other polyamines. The tripropylenetetramineemployed is preferably industrially obtainable tripropylenetetraminemixtures containing polyamines of the formulae ##STR1## and

    CH.sub.3 CH.sub.2 CH.sub.2 --NH--CH.sub.2 CH.sub.2 CH.sub.2 --NH--CH.sub.2 CH.sub.2 CH.sub.2 --NH--CH.sub.2 CH.sub.2 CH.sub.3

and the tetrapropylenepentamines employed are preferably industriallyobtainable tetrapropylenepentamine mixtures containing ##STR2## and

    H.sub.2 N--(CH.sub.2).sub.3 †NH--(CH.sub.2).sub.3 .brket close-st.NH--(CH.sub.2).sub.3 --NH.sub.2.

The polyoxyalkylene-polyols (b1) which can be used in accordance withthe invention can be prepared by known processes, for example by anionicpolymerization of one or more alkylene oxides having 2 to 4 carbon atomsin the presence of at least one of said initiator molecules, in absenceor preferably presence of a catalyst, for example an alkali metalhydroxide, such as sodium hydroxide or potassium hydroxide, or an alkalimetal alkoxide, such as sodium methoxide, sodium ethoxide, potassiumethoxide or potassium isopropoxide. In a specific preparation variant,the alkoxlation can first be carried out in the absence of catalysts,and the basic catalysts can be introduced into the reaction mixture withincreasing molecular weight of the novel polyoxyalkylene-polyols formed.Examples of suitable alkylene oxides are 1,2- and 2,3-butylene oxide,styrene oxide and preferably ethylene oxide and/or 1,2-propylene oxide.The alkylene oxides can be used here individually, or alternately oneafter the other or as a mixture.

For the production of the PU foams, preferably semirigid and rigid PUfoams, the novel polyoxyalkylene-polyols (b1) can be used as the onlyrelatively high-molecular-weight polyhydroxyl compound (b). However, inorder to modify the mechanical properties of the PU foams or fortechnical reasons associated with processing, it may be expedient touse, as polyhydroxyl compounds (b), mixtures containing at least onenovel polyoxyalkylene-polyol (b1) and at least one additionalpolyhydroxyl compound (b2) having a functionality of from 2 to 8, inparticular from 2 to 3, for semirigid PU foams and from 3 to 6 for rigidPU foams, and having a hydroxyl number of from 15 to 500, preferablyfrom 24 to 280, for semirigid PU foams and from 280 to 500 or more forrigid PU foams, with the exception of polyoxyalkylene-polyols as definedin (b1).

The mixtures of (b1) and (b2) preferred as polyhydroxyl compounds (b)have a hydroxyl number of from 30 to 500 and expediently contain, basedon the total weight of (b1) and (b2), from 0.1 to 50% by weight,preferably from 0.5 to 30% by weight, in particular from 1 to 10% byweight, of (b1), and from 99.9 to 50% by weight, preferably from 99.5 to70% by weight, in particular from 99 to 90% by weight, of (b2).

Relatively high-molecular-weight polyhydroxyl compounds (b2) which haveproven successful are, for example, polyoxyalkylene-polyols other than(b1), polyester-polyols, advantageously those prepared fromalkanedicarboxylic acids and polyhydric alcohols, polythioether-polyols,polyester-amides, hydroxyl-containing polyacetals, hydroxyl-containing,preferably aliphatic, polycarbonates or mixtures of at least two of saidpolyhydroxyl compounds. Preference is given to polyester-polyols and/or,in particular, polyoxyalkylene-polyols whose properties do not comeunder the definition of (b1).

Such polyoxyalkylene-polyols (b2) can be prepared by known processes,for example from one or more alkylene oxides having 2 to 4 carbon atomsin the alkylene radical by anionic polymerization using alkali metalhydroxides or alkoxides as catalysts and with addition of at least oneinitiator molecule containing from 2 to 8 reactive bonded hydrogenatoms, or by cationic polymerization using Lewis acids, such as antimonypentachloride, boron fluoride etherate inter alia, or bleaching earth ascatalysts.

Examples of suitable alkylene oxides for this purpose aretetrahydrofuran, 1,3-propylene oxide, 1,2- and 2,3-butylene oxide,styrene oxide and preferably ethylene oxide and 1,2-propylene oxide. Thealkaline oxides can be used individually, alternately one after theother or as mixtures. Examples of suitable initiator molecules are:water, organic dicarboxylic acids, such as succinic acid, adipic acid,phthalic acid and terephthalic acid, and preferably polyhydric, inparticular dihydric to octahydric alcohols or dialkylene glycols, forexample ethanediol, 1,2- and 1,3-propanediol, diethylene glycol,dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerol,trimethylolpropane, pentaerythritol, sorbitol and sucrose.

The polyoxyalkylene-polyols, preferably polyoxypropylene- andpolyoxypropylene-polyoxyethylene-polyols, expediently have, for theproduction of semirigid PU foams, a functionality of, preferably, from 2to 4, in particular from 2 to 3, and hydroxyl numbers of, preferablyfrom 24 to 160, and suitable polyoxytetramethylene glycols usually havea hydroxyl number of from 37 to 160.

Polyhydroxyl compounds (b2) which have proven highly successful are, forexample, polyoxyalkylene-polyols (b2) or mixtures thereof having afunctionality of from 2 to 4, preferably 2 to 3, and a hydroxyl numberof from 15 to 300, preferably from 15 to 280, in particular from 18 to260, prepared by polyaddition of ethylene oxide, 1,2-propylene oxide ormixtures of ethylene oxide and 1,2-propylene oxide onto at least oneinitiator molecule of the formula ##STR3## where R¹ and R² are identicalor different and are linear or branched C₁ - to C₄ -alkyl, the tworadicals together are C₄ - to C₆ -cycloalkylene, in which one methylenegroup may be replaced by an --O-- or --NR⁵ -- bridge, where R⁵ is C₁ -to C₄ -alkyl, or are identical or different and are dialkylaminoalkyl ofthe formula ##STR4## where R⁶ and R⁷ are identical or different and arelinear or branched C₁ -to C₄ -alkyl, or the two radicals together areC₄ - to C₆ -cycloalkylene, in which one methylene group may be replacedby an --O-- or --NR⁵ -- bridge, and X is an integer having a value of atleast 3,

z is an integer having a value of at least 3,

R³ is a C₂ - to C₄ -alkylene,

y is zero or a number from 1 to 3, and

R⁴ is hydrogen or C₁ - to C₄ -alkyl, with the proviso that y is zero ifR⁴ is hydrogen.

Preferred polyoxyalkylene-polyols (b2) having a functionality of from 2to 3 and a hydroxyl number of from 15 to 300, in particular from 18 to260, can be prepared, for example, by polyaddition of at least onealkylene oxide, preferably ethylene oxide, 1,2-propylene oxide or amixture of ethylene oxide and 1,2-propylene oxide, onto an initiatormolecule from the group consisting of N,N-dimethyl-1,3-diaminopropane,N,N-dimethyl-1,4-diaminobutane and in particularN,N-dimethyldipropylenetriamine. Highly reactive polyoxyalkylenepolyols(b2) of this type, in which the tertiary amino group is bonded to the--NH-- and/or --NH₂ groups which react with alkylene oxide via a spacerbridge comprising at least 3 methylene radicals, are described inDE-A-41 35 588, the entire disclosure content of which is incorporatedherein by way of reference.

Other preferred polyhydroxyl compounds (b2) are blockpolyoxypropylene-polyoxyethylene-polyols (b2) or mixtures thereof havinga hydroxyl number of from 15 to 65, preferably from 24 to 40, and acontent of terminal ethylene oxide units of from 2 to 9% by weight,preferably from 3 to 8% by weight, in particular from 5 to 7% by weight,based on the weight of the polyoxypropylene units, which are prepared byanionic polymerization of 1,2-propylene oxide onto an initiator moleculemixture having a mean functionality of from 2.3 to 2.8, preferably from2.3 to 2.7, in particular from 2.5 to 2.7, at elevated temperature,which comprises water and glycerol and/or trimethylolpropane, andpolymerization of ethylene oxide onto the resultant polyoxypropyleneadduct. Block polyoxypropylene-polyoxyethylene-polyols (b2) of said typehave been disclosed in EP-A-433 878 and EP-A-433 889, the entiredescriptions of which are incorporated herein by way of reference.

Other suitable polyhydroxyl compounds (b2) are polymer-modifiedpolyoxyalkylene-polyols (b2), preferably graft polyoxyalkylene-polyols,in particular those based on styrene and/or acrylonitrile, which areprepared by in-situ polymerization of acrylonitrile, styrene orpreferably mixtures of styrene and acrylonitrile, for example in aweight ratio of from 90:10 to 10:90, preferably from 70:30 to 30:70,expediently in the abovementioned polyoxyalkylene-polyols, as describedin German Patents 11 11 934, 12 22 669 (U.S. Pat. Nos. 3,304,273,3,383,351, 3,523,093), 11 52 536 (GB 1,040,452) and 11 52 537 (GB987,618), and polyoxyalkylene-polyol dispersions containing, asdispersant phase, usually in an amount of from 1 to 50% by weight,preferably from 2 to 25% by weight: for example polyureas,polyhydrazides, melamine and/or polyurethanes containing bonded tertiaryamino groups, which are described, for example, in EP-B-011 752 (U.S.Pat. No. 4,304,708), U.S. Pat. No. 4,374,209 and DE-A-32 31 497.

The polyoxyalkylene-polyols (b2) can be used individually or in the formof mixtures.

Other polyhydroxyl compounds (b2) which can be used arepolyester-polyols, which can be prepared, for example, fromalkanedicarboxylic acids having 2 to 12 carbon atoms, preferablyalkanedicarboxylic acids having 4 to 6 carbon atoms, or mixtures ofalkanedicarboxylic acids and/or aromatic polycarboxylic acids andpolyhydric alcohols, preferably diols, having 2 to 12 carbon atoms,preferably 2 to 6 carbon atoms, and/or alkylene glycols. Examples ofsuitable alkanedicarboxylic acids are: succinic acid, glutaric acid,adipic acid, suberic acid, azelaic acid, sebacic acid anddecanedicarboxylic acid.

Examples of suitable aromatic polycarboxylic acids are phthalic acid,isophthalic acid and terephthalic acid. The alkanedicarboxylic acids canbe used individually or as a mixture with one another. Instead of thefree dicarbxocylic acids, it is also possible to use the correspondingdicarboxylic acid derivatives, for example dicarboxylic acid monoestersor diesters with alcohols having i to 4 carbon atoms or dicarboxylicanhydrides. Preference is given to dicarboxylic acid mixtures comprisingsuccinic acid, glutaric acid and adipic acid, in mixing ratios of, forexample, from 20 to 35:35 to 50:20 to 32 parts by weight, in particularadipic acid. Examples of dihydric and polyhydric alcohols, in particulardiols or alkylene glycols, are: ethanediol, diethylene glycol, 1,2- and1,3-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, 1,10-decanediol, glycerol and trimethylolpropane.Preference is given to ethanediol, diethylene glycol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol and mixtures of at least two of the saiddiols,in particular mixtures of 1,4-butanediol, 1,5-pentanediol and1,6-hexanediol. It is also possible to employ polyester-polyols madefrom lactones, for example ε-caprolactone, or hydroxycarboxylic acids,for example ω-hydroxycaproic acid.

In order to prepare the polyester-polyols, the mixtures of aromatic andaliphatic dicarboxylic acids and preferably alkanedicarboxylic acidsand/or derivatives thereof and polyhydric alcohols can be polycondensedin the absence or preferably in the presence of esterificationcatalysts, expediently in an atmosphere of inert gases, for examplenitrogen, helium, argon inter alia, in the melt at temperatures of from150° to 250° C., preferably from 180° to 220° C., if desired underreduced pressure, to the desired acid number, which is advantageouslyless than 10, but preferably less than 2. In a preferred embodiment, theesterification mixture is polycondensed at the abovementionedtemperatures to an acid number of from 80 to 30, preferably from 40 to30, under atmospheric pressure and subsequently under a pressure of lessthan 500 mbar, preferably from 50 to 150 mbar. Examples of suitableesterification catalysts are iron, cadmium, cobalt, lead, zinc,antimony, magnesium, titanium and tin catalysts in the form of metals,metal oxides metal salts. However, the polycondensation can also becarried out in the liquid phase in the presence of diluents and/orentrainers, for example benzene, toluene, xylene or chlorobenzene, forazeotropic removal of the water of condensation by distillation.

In order to prepare the polyester-polyols, the organic polycarboxylicacids and/or derivatives thereof and polyhydric alcohols areadvantageously polycondensed in a molar ratio of from 1:1 to 1.8,preferably from 1:1.05 to 1.2.

The resultant polyester-polyols preferably have a functionality of from2 to 4, in particular from 2 to 3, and a hydroxyl number of from 24 to200, preferably from 32 to 140, in particular from 40 to 94.

Examples of suitable hydroxyl-containing polyacetals are the compoundswhich can be prepared from glycols, such as diethylene glycol,triethylene glycol, 4,4'-dihydroxyethoxydiphenyldimethylmethane,hexanediol and formaldehyde. Suitable polyacetals can also be preparedby polymerization of the cyclic acetals.

Examples of suitable hydroxyl-containing polycarbonates are those of thetype known per se, which can be prepared, for example, by reactingdiols, such as 1,3-propanediol, 1,4-butanediol and/or 1,6-hexanediol,diethylene glycol, triethylene glycol or tetraethylene glycol, withdiaryl carbonates, for example diphenyl carbonates, or phosgene.

The polyester-amides include, for example, the predominantly linearcondensates obtained from polybasic, saturated and/or unsaturatedcarboxylic acids or anhydrides thereof, and polyhydric, saturated and/orunsaturated aminoalcohols, or mixtures of polyhydric alcohols andaminoalcohols and/or polyamines.

c) The production of the PU foams by the novel process can also becarried out in the presence of low-molecular-weight, difunctional chainextenders, low-molecular-weight, trifunctional or polyfunctional,preferably trifunctional or tetrafunctional, crosslinking agents ormixtures of chain extenders and crosslinking agents, in addition to therelatively high-molecular-weight polyhydroxyl compounds (b).

Examples of suitable chain extenders and crosslinking agents (c) of thistype are diols, such as (cyclo)alkanediols and dialkylene glycols,and/or polyhydric alcohols, preferably triols and tetraols, havingmolecular weights of less than 400, preferably from 60 to 300. Examplesof suitable compounds are aliphatic, cycloaliphatic and/or araliphaticdiols having 2 to 14 carbon atoms, preferably 4 to 10 carbon atoms, forexample ethylene glycol, 1,3-propanediol, 1,10-decanediol, o-, m- andp-dihydroxycyclohexane, diethylene glycol, dipropylene glycol andpreferably 1,4-butanediol, 1,6-hexanediol andbis(2-hydroxyethyl)hydroquinone, and triols, such as 1,2,4- and1,3,5-trihydroxycyclohexane, glycerol and trimethylolpropane. Othersuitable chain extenders and crosslinking. linking agents arelow-molecular-weight, hydroxyl-containing polyalkylene oxides havingmolecular weights of up to 400 based on ethylene oxide and/or1,2-propylene oxide and, as initiator molecules, the diols and/or triolsmentioned by way of example.

If mixtures of relatively high-molecular-weight polyhydroxyl compounds(b) and chain extenders and/or crosslinking agents (c) are used, forexample to modify the mechanical properties, for example the hardness,these expediently contain the chain extenders and/or crosslinking agents(c) in an amount of from 0.5 to 20% by weight, preferably from 10 to 15%by weight, based on the total weight, the alkali ion content of themixture usually being less than 10 ppm, preferably less than 5 ppm, inparticular less than 3 ppm.

Other suitable crosslinking agents (c) are those having a high contentof alkali metal ions, preferably potassium ions, for example of from 150to 1200 ppm, preferably from 150 to 800 ppm, in particular from 400 to600 ppm.

d) The blowing agents (d) which can be used for the production of the PUfoams, preferably semirigid and rigid PU foams, preferably includewater, which reacts with isocyanate groups with formation of carbondioxide. The amounts of water expediently employed are from 0.1 to 8parts by weight, preferably from 1.5 to 5.0 parts by weight, inparticular from 2.5 to 3.5 parts by weight, based on 100 parts by weightof the polyhydroxyl compounds (b) or the mixtures of relativelyhigh-molecular-weight polyhydroxyl compounds (b) and chain extendersand/or crosslinking agents.

It is also possible to employ physical blowing agents, as a mixture withwater or as the only blowing agent. Suitable compounds are liquids whichare inert toward the organic, modified or unmodified polyisocyanate (a)and have boiling points of below 100° C., preferably below 50° C., inparticular from -50° to 40° C., at atmospheric pressure, so that theyevaporate under the effect of the exothermic polyaddition reaction.Examples of such preferred liquids are hydrocarbons, for example n- andisopentane, preferably technical-grade mixtures of n- and isopentane, n-and isobutane, n- and isopropane, cycloalkanes, for example cyclohexaneand cyclopentane, ethers, for example furan, dimethyl ether and diethylether, ketones, for example acetone and methyl ethyl ketone, alkylcarbonates, for example methyl formate, dimethyl oxalate and ethylacetate, and halogenated hydrocarbons, for example methylene chloride,dichloromonofluoromethane, difluoromethane, difluorochloromethane,trifluoromethane, trifluoroethane, tetrafluoroethane,heptafluoropropane, 1-chloro-2,2-difluoroethane (142),1-chloro-1,1-difluoroethane (142b) and 1-chloro-1,2-difluoroethane(142a). It is also possible to use mixtures of these low-boiling liquidswith one another, for example mixtures of difluorochloromethane and142b, and/or with other substituted or unsubstituted hydrocarbons.

The requisite amount, or the requisite amount in addition to water, ofphysical blowing agents can be determined in a simple manner as afunction of the desired foam density and is from about 0 to 25 parts byweight, preferably from i to 25 parts by weight, in particular from 2 to15 parts by weight, per 100 parts by weight of the polyhydroxylcompounds (b). It may be expedient to mix the modified or unmodifiedpolyisocyanates (a) with the inert, physical blowing agents and thus toreduce the viscosity.

e) The PU foams can be produced by the novel process in the absence ofconventional amine catalysts. However, the reaction is expedientlycarried out in the presence of conventional catalysts (e), which greatlyaccelerate the reaction of the organic and/or modified organicpolyisocyanates (a) with the polyhydroxyl compounds (b) and chainextenders and/or crosslinking agents (c). Examples of suitable catalystsare alkali metal salts of monocarboxylic acids containing linear orbranched alkyl radicals having 1 to 20 carbon atoms, preferably 1 to 18carbon atoms, and/or dicarboxylic acids containing linear or branchedalkyl radicals having 2 to 20 carbon atoms, preferably 2 to 12 carbonatoms, for example potassium formate, potassium acetate, potassiumoctanoate, potassium maleate and dipotassium adipate, and organometalliccompounds, preferably organotin compounds, for example tin(II) salts oforganic carboxylic acids, for example tin(II) diacerate, tin(II)dioctanoate, tin(II) diethylhexanoate and tin(II) dilaurate, and thedialkyltin(IV) salts of organic carboxylic acids, for example dibutyltindiacetate, dibutyltin dilaurate, dibutyltin maleate and dioctyltindiacetate. Such catalysts are described, for example, in DE-A-3 048 529.Dialkyltin(IV) mercapto compounds, for example bislauryltin(IV)dimercaptide, have also proven highly suitable.

The catalysts are usually used in an amount of from 0.001 to 0.2 part byweight, preferably from 0.005 to 0.015 part by weight, per 100 parts byweight of the formative components (a) to (c).

f) If desired, additives (e) can also be incorporated into the reactionmixture for the production of the PU foams, preferably semirigid andrigid PU foams. Examples which may be mentioned are acids, plasticizers,surfactants, foam stabilizers, cell regulators, fillers, antioxidants,dyes, pigments, flameproofing agents, antihydrolysis agents andfungistatic and bacteriostatic substances.

For the production of the PU foams by the novel process, inorganicacids, organic acids or mixtures of inorganic and organic acids can beused as preferred additive (f). Examples of inorganic acids which haveproven successful are polyphosphoric acids, monobasic and polybasicphosphoric acids, preferably triphosphoric acid, and hydrochloric acid.Preference is given to organic acids, in particular those from the groupconsisting of monocarboxylic acids, polycarboxylic acids, preferablydicarboxylic acids, and aromatic sulfonic acids. Organic acids which maybe mentioned by way of example are mono- and dicarboxylic acids, forexample formic acid, acetic acid, propionic acid and preferablyricinoleic acid, hydroxystearic acids, oxalic acids, succinic acid,maleic acid, fumaric acid, tartaric acid, citric acid, adipic acid,benzoic acid, phthalic acid, terephthalic acid and isophthalic acid, andsulfonic acids, for example benzenesulfonic acid and p-toluenesulfonicacid. Depending on their pKa value and molecular weight and on thebasicity of the polyhydroxyl compounds (b), the inorganic and/or organicacids are usually used in an amount of from 0.1 to 20 parts by weight,based on 100 parts by weight of polyhydroxyl compound (b), it beingpossible to determine the precise amounts by weight by simplepreliminary experiments.

Organic acids which have proven particularly successful are long-chainfatty acids, for example ricinoleic acid and hydroxyfatty acids, forexample hydroxystearic acids, which can be obtained from natural oils,and can be converted into hydroxyfatty acids by epoxidation of theunsaturated double bonds and adduction of monohydric and/or polyhydricalcohols onto the epoxide group. Hydroxyl-containing organic acids ofthis type have proven particularly successful in combination withcrosslinking agents (c) having a high content of alkali metal ions,since this combination has an excellent emuslification action and givesthe PU foams an extremely homogeneous foam structure. When acrosslinking agent (c) having an alkali metal ion content of less than10 ppm is used in combination with the organic acids, the cream time ofthe reaction mixture is extended.

Other additives (f) which have proven successful are plasticizers,which, inter alia, improve the flow behavior of the reaction mixture.Suitable examples are plasticizers from the group consisting of dialkylphthalates, for example those having 4 to 20 carbon atoms, preferably 9to 11 carbon atoms, in the alkyl radical. These plasticizers arecommercially available under the trade name Palatinol® from BASFAktiengesellschaft. Other suitable plasticizers are phosphates, forexample tricresyl phosphate, phenyl dicresyl phosphate, inter alia,which simultaneously improve the flame resistance of the PU foams.

Examples of suitable surfactants are compounds which serve to supporthomogenization of the starting materials and may also be suitable forregulating the cell structure. Examples which may be mentioned areemulsifiers, such as sodium salts of castor oil sulfates or of fattyacids, and salts of fatty acids with amines, for example diethylamineoleate, diethanolanane stearate, diethanolamine ricinoleate, salts ofsulfonic acids, for example alkali metal or ammonium salts ofdodecylbenzene- or dinaphthylmethanedisulfonic acid and ricinoleic acid;foam stabilizers, such as siloxane-oxyalkylene copolymers and otherorganopolysiloxanes, oxyethylated alkylphenols, oxyethylated fattyalcohols, paraffin oils, esters of castor oil and ricinoleic acid,turkey red oil and groundnut oil, and cell regulators, such asparaffins, fatty alcohols and dimethylpolysiloxanes. Furthermore, theemulsification action and cell structure can be improved and/or the foamcan be stabilized using oligomeric polyacrylates containingpolyoxyalkylene and fluoroalkane radicals as side groups. Thesurfactants are usually used in amounts of from 0.01 to 5 parts byweight, based on 100 parts by weight of polyhydroxyl compounds (b) andchain extenders and/or crosslinking agents (c).

For the purposes of the present invention, the term fillers, inparticular reinforcing fillers, is taken to mean conventional organicand inorganic fillers and reinforcing materials known per se. Specificexamples which may be mentioned are: inorganic fillers, such as silicateminerals, for example phyllosilicates, such as antigorite, serpentine,hornblende, amphibole, chrisotile, zeolites and talc; metal oxides, suchas kaolin, aluminum oxides, aluminum silicate, titanium oxide and ironoxides, metal salts, such as chalk, barytes and inorganic pigments, suchas cadmium sulfide and zinc sulfide, and glass particles. Examples ofsuitable organic fillers are: carbon black, melamine, collopbony,cyclopentadienyl resins and graft polymers.

The inorganic and organic fillers can be used individually or asmixtures and are advantageously incorporated into the reaction mixturein amounts of from 0.5 to 50% by weight, preferably from 1 to 40% byweight, based on the weight of the components (a) to (c).

Examples of suitable flameproofing agents are tricresyl phosphate,tris(2-chloroethyl) phosphate, tris(2-chloropropyl) phosphate,tris(1,3-dichloropropyl) phosphate, tris(2,3-dibromopropyl) phosphateand tetrakis(2-chloroethyl)ethylene diphosphate.

In addition to the abovementioned halogen-substituted phosphates, it isalso possible to use inorganic flameproofing agents, such as redphosphorus, aluminum oxide hydrate, antimony trioxide, ammonium sulfate,ammonium polyphosphate and calcium sulfate, expandable graphite, urea orcyanuric acid derivatives, for example melamine or melamine cyanurate,or mixtures of at least two flameproofing agents, for example ammoniumpolyphosphates and melamine and, if desired, expandable graphite and/orstarch for flameproofing the PU foams produced according to theinvention. In general, it has proven expedient to use from 5 to 50 partsby weight, preferably from 5 to 25 parts by weight, of saidflameproofing agents or mixtures per 100 parts by weight of components(a) to (c).

Examples of antioxidants which can be used are non-volatilecryptophenols, for example the commercial products Irganox® 245 andIrganox® 1135 from Ciba/Geigy, or sterically hindered amines, forexample the commercial product Naugard® 445 from Uniroyal.

Further details on the other conventional auxiliaries mentioned aboveare given in the specialist literature, for example the monograph by J.H. Saunders and K. C. Frisch, High Polymers, Volume XVI, Polyurethanes,parts 1 and 2, Inter-science Publishers, 1962 and 1964 respectively, orthe Kunst-stoff-Handbuch, Polyurethane, Volume VII, Carl-Hanser-Verlag,Munich, Vienna, 1st and 2nd Editions, 1966 and 1983 respectively.

In order to produce the PU foams, preferably semirigid and rigid PUfoams, the organic, modified or unmodified polyisocyanates (a), thepolyhydroxyl compounds (b) and, if used, chain extenders and/orcrosslinking agents (c) are reacted in the presence of the blowingagents (d) and, if used, catalysts (e) and additives (f), usually atfrom 0° to 120° C., preferably at from 15° to 100° C., in particular atfrom 18° to 80° C., expediently in such amounts that advantageously from0.5 to 2, preferably from 0.8 to 1.3, in particular approximately one,hydroxyl group(s) is bonded to (b) or (b) and (c) per NCO group. Ifwater is used as one of the blowing agents or as the only blowing agent,it has proven expedient to use a ratio of, advantageously, from 0.5 to5:1, preferably from 0.7 to 0.95:1, in particular from 0.75 to 0.85:1,equivalents of water to equivalents of NCO groups. For the production ofPU foams containing isocyanurate groups, an NCO:OH group ratio of from 2to 25:1, preferably from 2 to 10:1, in particular from 2 to 5:1, forexample, has proven successful.

The PU foams, preferably the semirigid and rigid PU foams, areexpediently produced by the one-shot process by mixing two components Aand B, where formative components (b) and (d) and, if used, (c), (e) and(f), are usually combined to form component A, and the organic and/ormodified organic polyisocyanates (a), if desired mixed with inert,physical blowing agents, are used as component B. Components A and Bneed only be mixed vigorously before production of the PU foams. Thereaction mixture can be foamed and allowed to cure in open or closedmolds. Furthermore, prefabricated covering materials can be foam-backedto give moldings.

The novel process is also particularly suitable for the production of PUmolded foams. In this case, the reaction mixture, at from 15° to 80° C.,preferably from 30° to 65° C., is introduced into an expedientlymetallic, thermostatable mold temperature is usually from 20° to 90° C.,preferably from 35° to 70° C. The reaction mixture is usually allowed tocure without pressure or with compaction, for example at degrees ofcompaction of from 1.1 to 8, preferably from 2 to 6, in particular from2.2 to 4, in the closed mold.

The PU foams produced by the novel process usually have densities offrom 0.025 to 0.25 g/cm³, preferably from 0.035 to 0.08 g/cm³, it alsobeing possible for molded foams, for example those having a cellularcore and a compacted peripheral zone, to have densities of from 0.08 to0.75 g/cm³, preferably from 0.2 to 0.6 g/cm³, depending on the degree ofcompaction used. The PU foams produced by the novel process are, asstated above, essentially odorless, have a uniform, essentiallyvoid-free cell structure and have a uniformly high mechanical propertylevel.

The reaction mixtures for the production of the PU foams are used, forexample, in the vehicle industry, for example in the automotive,aircraft and shipbuilding industries, and in the refrigeration andconstruction industries for foam-filling and foam-backing of cavities,for example dashboards and control panels, as interlayers for sandwichelements or for foam-filling refrigerator and freezer casings. The PUfoams are suitable as insulation materials, for example as lagging forpiping or heating systems. They are also used as wall linings, housingparts, cushioning materials, armrests, headrests, sun visors, parcelshelves, glove boxes, safety covers and central consoles.

EXAMPLES Example 1

Component A: a mixture comprising

33.85 parts by weight of a block polyoxypropylene-polyoxyethylene-polyolhaving a hydroxyl number of 30 and a content of terminal ethylene oxideunits of 5.9% by weight, based on the weight of the propylene oxideunits, obtained by alkoxylation of an initiator molecule mixturecomprising glycerol and water in a weight ratio of 1:0.98,

0.25 part by weight of a glycerol-initiated polyoxyethylene (62.5% byweight)-polyoxypropylene (27.5% by weight)-polyoxyethylene (10% byweight)-polyol having a hydroxyl number of 42,

35.00 parts by weight of a 1,2-propylene glycol-initiatedpolyoxypropylene (81.5% by weight)-polyoxyethylene (18.5% by weight)glycol having a hydroxyl number of 29,

6.00 parts by weight of anN,N,-bis(3-aminopropyl)ethylenediamine-initiated polyoxypropylene-polyolhaving a hydroxyl number of 393,

1.6 parts by weight of ricinoleic acid, 20.0 parts by weight of adi(C₉ - to C₁₁ -alkyl)phthalate, 2.2 parts by weight of water,

0.45 part by weight of a 40% strength by weight potassium acetatesolution in ethylene glycol,

0.40 part by weight of black paste and

1.0 part by weight of a sterically hindered amine as antioxidant(Naugard® 445).

Component B: A mixture of diphenylmethane diisocyanate isomers andpolyphenyl-polymethylene polyisocyanates having an NCO content of 31.3%by weight and a diphenylmethane diisocyanate isomer content of 39% byweight, based on the total weight.

Foam backing of a dashboard for a motor vehicle:

This is carried out using a Hennecke foaming apparatus fitted with an MQmixing head with throttle setting 5, nozzles having a diameter of 1.3 mmfor component A and of 0.8 mm for component B, and an output capacity of223 g/sec. The shot time was 4.2 to 5.05 seconds, corresponding to anoutput of 920 to 1126 g.

For foam-backing of the dashboards, the PVC/ABS cover film was placed ina metallic mold thermostated at from 40° to 43° C., the mold was closed,components A and B were mixed in a weight ratio of 100:43 at 30° C. at200 bar, and the reaction mixture was injected into the closed mold,where it was allowed to expand.

The resultant dashboard was demolded after 3.5 minutes and then storedat 80° C. for 1 hour. There was no evidence of any sink marks. After 24hours, the molding exhibited excellent adhesion between the semirigid PUfoam and the PVC/ABS film.

30 avoid-free dashboards were produced without problems by the proceduredescribed. The series experiment was then terminated.

The reaction mixture had a setting time of 70 seconds and a rise time of105 seconds. The PU foam had a free-foamed density of 76 g/l.

Example 2

Component A: a mixture comprising

47.50 parts by weight of a block polyoxypropylene-polyoxyethylene-polyolhaving a hydroxyl number of 30 and a content of terminal ethylene oxideunits of 5.9% by weight, based on the weight of the propylene oxideunits, obtained by alkoxylation of an initiator molecule mixturecomprising glycerol and water in a weight ratio of 1:0.98,

1.50 parts by weight of a glycerol-initiated polyoxyethylene (62.5% byweight)-polyoxypropylene (27.5% by weight)-polyoxyethylene (10% byweight)-polyol having a hydroxyl number of 42,

42.3 parts by weight of a glycerol-initiated polyoxypropylene (86% byweight)-polyoxyethylene (14% by weight)-polyol having a hydroxyl numberof 28,

1.00 parts by weight of a polyoxypropylene-polyol having a hydroxylnumber of 394 initiated by means of technical gradetripropylenetetramine,

5.00 parts by weight of an N,N-dimethyl-1,3-diaminopropane-initiatedpolyoxypropylene-polyol having a hydroxyl number of 250,

0.5 part by weight of ricinoleic acid,

2.2 parts by weight of water and

1.0 part by weight of a sterically hindered amine as antioxidant(Naugard® 445).

Component B: as in Example 1.

The molding was produced by a method similar to that of Example 1, butcomponents A and B were mixed in a weight ratio of 100:41.66.

The molding, demolded after 3 minutes, exhibited no sink marks or voids.

The reaction mixture had a setting time of 78 seconds and a rise time of108 seconds. The PU foam had a free-foamed density of 66 g/l.

Example 3

Component A: a mixture comprising

42.6 parts by weight of a block polyoxypropylene-polyoxyethylene-polyolhaving a hydroxyl number of 30 and a content of terminal ethylene oxideunits of 5.9% by weight, based on the weight of the propylene oxideunits, obtained by alkoxylation of an initiator molecule mixturecomprising glycerol and water in a weight ratio of 1:0.98,

43.95 parts by weight of an N,N-dimethyldipropylenetriamine-initiatedpolyoxypropylene (86.5% by weight)-polyoxyethylene (13.5% byweight)-polyol having a hydroxyl number of 35,

3.3 parts by weight of a graft polyether-polyol having a hydroxyl numberof 28, prepared by free-radical, in-situ polymerization of aglycerol-initiated polyoxypropylene-polyoxyethylene-polyol as graft baseand a mixture of styrene and acrylonitrile in a weight ratio of 3:2 forformation of the graft (Lupranol® 4100 from BASF Aktiengesellschaft),

4.0 parts by weight of a glycerol-initiated polyoxyethylenepolyol havinga hydroxyl number of 525 and a potassium ion content of 470 ppm,

2.0 parts by weight of a polyoxypropylene-polyol having a hydroxylnumber of 386 initiated by means of technical gradetetrapropylenepentamine,

1.6 parts by weight of ricinoleic acid,

2.0 parts by weight of water,

0.15 part by weight of black paste and

1.0 part by weight of a sterically hindered amine as antioxidant(Naugard® 445).

Component B: as in Example 1.

The dashboard was produced by a method similar to that of Example 1, butcomponents A and B were mixed in a weight ratio of 100:45.

The dashboard, demolded after 2.5 minutes, exhibited no sink marks orvoids in the semirigid PU foam.

The reaction mixture had a setting time of 77 seconds and a rise time of115 seconds. The PU foam had a free-foamed density of 79 g/l.

Example 4

Component A: as in Example 2, but the 1 part by weight ofpolyoxypropylene-polyol initiated by means of technical gradetripropylene tetramine was replaced by 1 part by weight of an

N,N'-bis(3-aminopropyl)ethylenediamine-initiated polyoxypropylene-polyolhaving a hydroxyl number of 352.

Component B: as in Example 1.

The molding was produced by a method similar to that of Example 1, butcomponents A and B were mixed in a weight ratio of 100:44.

The molding, demolded after 3 minutes, exhibited no sink marks or voidsin the PU foam.

The reaction mixture had a setting time of 76 seconds and a rise time of110 seconds. The PU foam had a free-foamed density of 76 g/l. Thefogging value, measured in accordance with DIN 75 201, Method B, was0.03 mg.

Comparative Example

Production of semirigid PU foams

Component A: a mixture comprising

82.4 parts by weight of a polyoxypropylene-polyol having a hydroxylnumber of 400, prepared using an initiator molecule mixture comprisingsucrose and water,

3.6 parts by weight of water,

10.9 parts by weight of cyclopentane,

2.3 parts by weight of dimethylaminocyclohexylamine and

0.8 part by weight of a silicone-based foam stabilizer

(Tegostab® 8409 from Goldschmidt AG).

Component B: as in Example 1.

In order to produce a molding, components A and B were mixed in a weightratio of 100:147.14, and the reaction mixture was transferred into ametallic mold and allowed to expand and cure.

The rigid PU foam molding, demolded after 3 minutes, was brittle andunsuitable for industrial use.

The reaction mixture had a cream time of 14 seconds, a setting time of54 seconds and a rise time of 72 seconds. The PU foam had a free-foameddensity of 25.4 g/l. Example 5

Component A=a mixture comprising

84.7 parts by weight of anN,N'-bis(3-aminopropyl)ethylenediamine-initiated polyoxypropylene-polyolhaving a hydroxyl number of 407,

3.6 parts by weight of water,

10.9 parts by weight of cyclopentane and

0.8 part by weight of a silicone-based foam stabilizer (Tegostab® 8409from Goldschmidt AG).

Component B: as in Example 1.

The molding was produced by a method similar to that of the ComparativeExample, but components A and B were mixed in a weight ratio of100:151.16.

The non-brittle rigid PU foam of the industrially suitable molding,which was demolded after 3 minutes, was extremely fine-celled.

The reaction mixture had a cream time of 8 seconds, a setting time of 23seconds and a rise time of 37 seconds. The PU foam had a free-foameddensity of 25.8 g/l.

We claim:
 1. A process for the production of polyurethane foams byreactinga) at least one organic polyisocyanate with b) at least onerelatively high-molecular-weight polyhydroxyl compound containing atleast two reactive hydrogen atoms and c) optionally,low-molecular-weight chain extenders and/or crosslinking agents,in thepresence of d) blowing agents, wherein the polyhydroxyl compound (b)comprises a polyoxyalkylene-polyol (b1) having a hydroxyl number of from30 to 500, obtainable by alkoxylation of at least one initiator moleculefrom the group consisting of N,N'-bis(3-aminopropyl)ethylenediamine,tripropylenetetramine and tetrapropylenepentamine using at least onealkylene oxide.
 2. A process as claimed in claim 1, wherein thetripropylenetetramine used comprises a technical-gradetripropylenetetramine mixture comprising ##STR5## and

    CH.sub.3 CH.sub.2 CH.sub.2 --NH--CH.sub.2 CH.sub.2 CH.sub.2 --NH--CH.sub.2 CH.sub.2 CH.sub.2 --NH--CH.sub.2 CH.sub.2 CH.sub.3.


3. A process as claimed in claim 1, wherein the tetrapropylenepentamineused is a technical-grade tetrapropylenepentamine mixture comprising##STR6## and

    H.sub.2 N--(CH.sub.2).sub.3 .brket open-st.NH--(CH.sub.2).sub.3 .brket close-st.NH--(CH.sub.2).sub.3 --NH.sub.2.


4. A process as claimed in claim 1, wherein the alkylene oxide(s) is(are) ethylene oxide or 1,2-propylene oxide or ethylene oxide and1,2-propylene oxide.
 5. A process as claimed in claim 1, wherein thepolyhydroxyl compound used is a mixture comprisingb1) at least onepolyoxyalkylene-polyol having a hydroxyl number of from 30 to 500,obtainable by alkoxylation of at least one initiator molecule from thegroup consisting of N,N'-bis(3-aminopropyl)ethylenediamine,tripropylenetetramine and tetrapropylenepentamine, or technical-grademixtures thereof, using at least one alkylene oxide and b2) at least onepolyhydroxyl compound having a functionality of from 2 to 8 and ahydroxyl number of from 15 to 500, with the exception ofpolyoxyalkylene-polyols as defined in (b1).
 6. A process as claimed inclaim 1, wherein the polyhydroxyl compound used is a mixture comprising,based on the total weight of (b1) and (b2),b1) from 0.1 to 50% by weightof at least one polyoxyalkylene-polyol having a hydroxyl number of from30 to 500, obtainable by alkoxylation of at least one initiator moleculefrom the group consisting of N,N'-bis(3-aminopropyl)ethylenediamiene,tripropylenetetramine and tetrapropylenepentamine, or technical-grademixtures thereof, using at least one alkylene oxide and b2) from 99.9 to50% by weight of at least one polyhydroxyl compound having afunctionality of from 2 to 8 and a hydroxyl number of from 15 to 500,with the exception of polyoxyalkylene-polyols as defined in (b1).
 7. Aprocess as claimed in claim 1, wherein the blowing agent is water.
 8. Aprocess as claimed in claim 1, wherein the polyurethane foams areproduced in the presence ofe) catalysts and f) additives.
 9. A processas claimed in claim 1, wherein the polyurethane foams are produced inthe presence of ricinoleic acid, hydroxyfatty acids and/or dialkylphthalates having 4 to 20 carbon atoms in the alkyl radical asadditives.